Basic refractory structure



Nov. 30, 1948; E. c. HITE V 2,454,922

BASIC REFRACTORY S'iiiUCTURES Filed July 31. 1943 Basrc Bmcx,

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INVENTOK ifs/5257'? C. H175:

, Thus, a standard Patented Nov. 30, 1948 BASIC REFRACTORY STRUCTURE Everett C. Rite, Canton,

Timken Roller Bearln Ohio, assignor to The B Company, Canton,

Ohio, a corporation of Ohio Application July 31, 1943, Serial No. 496,949

. 8 Claims. I

This invention relates to refractory structures constructed from basic refractory brick.

Although the invention is applicable to all types of refractory structures, such as walls and linings of furnaces, it is particularly adapted to arched roofs for which reason it may be described with particular reference thereto, although not by way of limitation.

It is characteristic of basic brick that they expand progressively upon being heated to suecessively higher temperatures, and further that in being heated to high temperatures, for example such as are encountered in electric furnace roofs, the total expansion is considerable. practice is to allow as much as A; or of an inch per foot for expansion of basic refractory brick. Expansion of, silica brick is provided for adequately in many cases by disposing a sheet of combustible matter, such as cardboard, between the bricks, but this practice is not satisfactory with basic brick.

The reason cardboard is satisfactory with silica brick is that most of its expansion occurs within a relative narrow range of temperature relatively close to the temperature at which the cardboard is completely burned out. In contrast, basic bricks continue to expand throughout the entire range over which they are heated. The result of this in attempting to use cardboard with basic brick may be described with referenceto an arch roof of an electric furnace. By the time the cardboard has burned out,- say as the roof is heated to 800 to 1200 F., only a part of the total expansion has occurred, of the cardboard the roof then slumps. As the roof is then heated further up to operating temperature, say 2900 or 3000' F., the bricks continue to expand progressively, and now the roof bulges, either non-uniformly or to an undesired extent. Such consequences are objectionable.

I Also, such combustible matter does not produce bonding, and for many purposes it is desirable that these basic brick structures be bonded.

. That might be done by mortars, but the basic brick mortars available heretofore do not produce bonding or cementing of the bricks, nor do they provide for expansion, and unless provision is made for expansion the ends of the bricks which are exposed to heat may, and commonly will, spall, which is highly undesirable because, amongother things, it shortens the useful life of the structure.

For a considerable number of years it has been known that basic brick can be bondedsatisfactorily by means of sheet iron disposed between and in consequence of burning out the bricks, and by laying the brick up loosely in that manner provision is made to some extent for expansion upon heating. Although that practice It is an object of this invention to provide a method of bonding basic refractory structures which is simple, easily performed, and inexpensive, and which not only provides effective and adequate bonding of the bricks into, effectively, a unitary structure without deleterious fluxing, but also provides for expansion of the basic refractory shapes upon initial heating of the structures.

Another object is to provide a refractory structure comprising basic brick which is simple, relatively inexpensive, produced readily from easily available and cheap material, and which combines desirable bonding of the bricks with automatic compensation for expansion of the brick in producing such bonding.

Yet another object is to provide a refractory structure comprising basic brick bonded with fusion product of asbestos, and particularly one in which the bricks are bonded by reaction product of the bricks and fusion product of asbestos, while avoiding undesirable fiuxing'of the bricks.

Still another object is to provide basic bricks which upon being heated in a structure built from them will produce an autogenous bond when the structure is heated to at least about2600 F.,

without objectionable Other objects will lowing description.

The drawing is a representation of a portion of a furnace wall in accordance with this invention. I have discovered, and it is upon this that the invention is in large part predicated, that a layer of bricks, or other shapes, produces satisfactory bonding of the bricks when a structure built in that manner is heated to a sufficiently high, temperature. The term basic brick as used herein has a well understood meaning in the refractory art, and it includes, for example, magnesite bricks, both burned and unburned, chrome ore bricks, chrome-magnesite bricks, and forsterite (magnesium orthosilicate) bricks.

fiuxing of the bricks. be understood from the fol asbestos disposed between basic refractory,

assembly without waste of be supplied.

be satisfactory for the purposes of the invention are as follows:

. Foo, e10. 050, M 0, 1.1.0,, m g fggigg, Per Per Per Per Per F Per Qent Cent Cent Cent Cent g d The asbestos may be applied to the bricks in the form of a mortar, for example by mixing loose asbestos fiber with water or with a water solution of a suitable binder such as sodium silicate, dextrine, molasses, lignin liquor or the like. For most purposes it is preferred, however, to insert between the bricks or other shapes one or more sheets of the commercially available asbestos pa- Most suitably the sheet and board to size for ease and rapidity of material. r The thickness of the asbestos layer to be supplied will depend upon the amount of expansion for which provision must be made, and this will depend, as will be understood, upon the particular composition of the basic refractory, the type of the structure, and the temperatures to which it will be exposed. Asbestos paper weighing 32 lbs. per 100 sq. ft. is of such thickness that four layers will produce a inch joint. Asbestos board is available in a variety of thicknesses, greater than those of the sheet form. It will be evident, therefore, that by the use of one or more sheets of paper or of one or more sheets of board. or of board and paper, any desired width of joint can For most purposes it is preferred to apply the asbestos between all of the bricks. If desired, the asbestos material may be cepers orboards. material are cut mented to the bricks or other shapes at the plant where they are made so that in the field it is necessary only to laythem up into the structure being erected or repaired. This can be done easily by the use of adhesives such as those identified above, and where sodium silicate is'used for this purpose the amount does not have any detrimental fluxing efiect. For example, one or moresheets of asbestos may be applied to one or more faces of the molds used for pressing the bricks. Most suitably all of the brick faces (exclusive of the ends) will be covered in this manner.

When a structure built in this manner is heated the asbestos undergoes shrinkage due, presumably, to loss of moisture and chemically combined water. This phenomenon begins in the range of temperature in which it becomees necessary to provide for expansion, Thus the invention provides not only for adequate bonding of basic bricks, but also expansion during heating productive of bonding is automatically compensated, which is of real importance. Expansion of the bricks is thus taken care of satisfactorily with avoidance of pinching and spalling which prolongs the life of the structure.

I have found that when heated to a sufilcientiy high temperature the asbestos bonds these basic bricks strongly and without obiectionablefluxing, due, I believe. to the following factors. At about 2800 F. the commercial grades of asbestos begin to fuse with formation of forsterite, clinoenstatite, and a small amount of a silica glass. As the temperature is raised further the amount of liquid increases progressively, and in the presence of magnesia, which is present in many basic bricks, further {amounts of .forsterite will form. This fusion behavior of asbestos is particularly favorable to the present invention because forsterite is highly refractory, it is basic and therefore does not exert any fiuxing action on the bricks, and it produces bonding of the bricks. In

, any event, the bonding is due to fusion product of asbestos, it does not cause any detrimental fluxlng of the bricks, and I believe that it is due 'to reaction between the fusion products of the asbestos and constituents of the bricks.

The accompanying drawing shows, somewhat schematically, a portion of a furnace wall in accordance with this invention. Sheet asbestos is disposed between the contiguous faces and sides of magnesite or other basic bricks. ,The erected structure is heated to at least about 2600 F.

whereupon bonding of the bricks occurs, as just described, with production of the structure shown.

This mode of constructing and bonding refractory structures is cheaper than where those results are achieved through the use of sheet iron, and it is not substantially more expensive and is more desirable than where cardboard or similar burn-out material is used.

The exact temperature at which bonding occurs depends, as will be understood, upon the v. particular type of basic bricks that are used. For

instance, I have found by actual test that forsterite brick and chrcme-magnesite brick with asbestos interposed between them undergo some bonding at about 2600" F., and that good bonding is accomplished by heating them to2700 F. on the other hand, both burned and unburned magnesite are bonded excellently when they are heated to 2800 F., in the practice of this invention. Under the same conditions chrome and chrome-magnesite bricks also develop a strong bond. Heating to 2900 F., causes production of very tenacious asbestos bonds with all types of basic bricks that are commercially available.

The bonding temperature might be lowered by admixing the asbestos with fluxes, such as iron oxide, either by'adding the flux to an asbestos mortar or by incorporating it in asbestos sheet or board during its manufacture.

This action of asbestos in accordance with the invention iscontrary to what would have been expected. Thus, asbestos is not classed as a refractory, and the A.S.T.M. sets 900 F. as the maximum temperature to which ordinary asbestos sheet should be exposed. It might have been expected, therefore, that either the low refractoriness of asbestos would be objectionable, or that it might undesirably r'iux the bricks. Quite to the contrary, asbestos accomplishes satisfactory bonding of basic bricks without fluxing. And this action is peculiar to basic bricks because, as I have found by experience, asbestos'can not be used with acid brick for this purpose because in contact with silica brick it exerts a fiuxing action which is progressive and in time will be ultimately destructive of the bricks due to the formation of a glass which penetrates thebricks to a considerable distance.

According to the provisions of the patent statutes, I have explained the principle and mode of practicing my invention, and have described what I now consider to represent its best embodi- 5 that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

I claim:

- 1. In the'construction of a refractory structure 5 from basic brick, the improvement which consists in providing a layer of asbestos between ad- Jacent bricks, and heating said structure to a temperature of at least about 2600 F. and thereby fusing said asbestos and bonding the bricks. 1

2. A refractory structure comprising basic bricks bonded together with fusion product of asbestos.

3. A refractory structure comprising basic bricks bonded together by forsterite produced by fusion of asbestos between the bricks.

4. A refractory structure comprising basic bricks bonded together with reaction product of said bricks and fusion product of asbestos.

5. A method according to claim 1, said bricks being forsterite bricks.

6. A structure according to claim 2, said bricks being forsterite bricks.

7. A refractory structure comprising forsterite bricks bonded together by forsterite produced by fusion of asbestos between the bricks.

- being forsterite bricks.

8. A structure according to claim 4, said bricks EVERETT C. HITE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS OTHER REFERENCES Refractory Materials: Their Manufacture and Uses"; Searle 2nd edit., Rev.; published by Charles Griflln 8: Co., Ltd. London. Searle, 389, 587, 590, 591 and 592. y

Hicks Dec. 17, 1940 

